Relationship between Environmental Factors and Radar Amplitude: Illinois Basin – Decatur Project case study

2023 was claimed as the beginning of the “Global Boiling Era”. For this reason, geo-energies are key to provide a green and clean future. Geothermal energy, and geologic carbon injection/storage are the main types of geo-energies. Both have in common the underground fluid movement and the consequent ground motion dynamics.

One of the main techniques for analyzing ground motion is Persistent Scattered Interferometry (PSI), which allows us to estimate ground deformation over time from radar satellite data. PSI techniques calculate the temporal displacement in the so-called persistent scatterers by filtering the data based on amplitude value. Generally, the main cause for amplitude variability is the change in the surface properties over time, primarily due to changes in environmental factors (land cover/land use, vegetation dynamics, temporal water presence, or soil moisture). The main concern with these changes is that they may result in phase shifts, which could be misinterpreted as range displacements.

Improving the understanding of the environmental factors could improve the understanding of ground deformation over time. Therefore, environmental factors analysis and PSI can be integrated seamlessly into a workflow since the launch of the Copernicus Programme, combining Sentinel-1 and Sentinel-2 data. The goal of this research is to explore the relationship between environmental variables and amplitude values. This research is framed in the MultidiSciplinary and MultIscale approach for assessing coupLed processes induced by geo-Energies (SMILE) Project. The study site is the Illinois Basin – Decatur Project (IBDP), which is a carbon dioxide injection and storage located in the United States. IBDP is in the north part of Decatur city, the vegetation is mainly woodland and prairie; with a humid subtropical climate, with an annual precipitation over 1000 mm.

The analysis focuses on three areas near IBDP: wetland area, crop area, and woodland area. Performing a spatio-temporal analysis of the vegetation index (NDVI), soil moisture index (NDWI), and temporal water presence (NDWI) obtained from Sentinel-2 data between 2015 to 2023 and comparing these datasets with the amplitude time series from Sentinel-1 imagery for the same period. The results show that the woodland area has a high mean amplitude value with low dispersion; the wetland area has a low mean amplitude value with high dispersion; and the crop area has a medium mean amplitude value with medium dispersion.

The vegetation index for the woodland area has 7 month per year values over 0,4, showing a presence of high photosynthetic activity, which can be related to the low value of dispersion amplitude; while the wetland area only 3 months per year has a value over 0,4, that can be source of the high dispersion amplitude. While the crop area is 6 months over the threshold. The results of the analysis performed showed that the use of environmental indices can help in the interpretation of the dispersion amplitude in the PSI analysis. The next step is to consider more environmental variables such as snow cover, land cover/land use, or temperature in the analysis of amplitude, as well as consider different polarizations, among others.